CA1287464C - Heat-sealable multi-layer polypropylene film structure - Google Patents
Heat-sealable multi-layer polypropylene film structureInfo
- Publication number
- CA1287464C CA1287464C CA000490265A CA490265A CA1287464C CA 1287464 C CA1287464 C CA 1287464C CA 000490265 A CA000490265 A CA 000490265A CA 490265 A CA490265 A CA 490265A CA 1287464 C CA1287464 C CA 1287464C
- Authority
- CA
- Canada
- Prior art keywords
- layer
- ethylene
- film
- skin layer
- propylene
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B27/00—Layered products comprising a layer of synthetic resin
- B32B27/06—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material
- B32B27/08—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B27/00—Layered products comprising a layer of synthetic resin
- B32B27/18—Layered products comprising a layer of synthetic resin characterised by the use of special additives
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B27/00—Layered products comprising a layer of synthetic resin
- B32B27/32—Layered products comprising a layer of synthetic resin comprising polyolefins
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B2264/00—Composition or properties of particles which form a particulate layer or are present as additives
- B32B2264/10—Inorganic particles
- B32B2264/102—Oxide or hydroxide
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B2307/00—Properties of the layers or laminate
- B32B2307/30—Properties of the layers or laminate having particular thermal properties
- B32B2307/31—Heat sealable
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B2307/00—Properties of the layers or laminate
- B32B2307/50—Properties of the layers or laminate having particular mechanical properties
- B32B2307/514—Oriented
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B2310/00—Treatment by energy or chemical effects
- B32B2310/04—Treatment by energy or chemical effects using liquids, gas or steam
- B32B2310/0409—Treatment by energy or chemical effects using liquids, gas or steam using liquids
- B32B2310/0436—Oil
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B2323/00—Polyalkenes
- B32B2323/10—Polypropylene
Landscapes
- Laminated Bodies (AREA)
- Manufacture Of Macromolecular Shaped Articles (AREA)
- Connection Of Batteries Or Terminals (AREA)
- Prostheses (AREA)
- Blow-Moulding Or Thermoforming Of Plastics Or The Like (AREA)
- Materials For Medical Uses (AREA)
Abstract
HEAT-SEALABLE MULTI-LAYER POLYPROPYLENE FILM STRUCTURE Abstract A multi-layer film structure having antistick characteristics over a wide temperature range during heat-sealing, comprises an amine containing polypropylene core layer and one or more skin layers of a low stereoregularity polyolefin containing silica and a polysiloxane, the or each skin layer being less than 0.8 micron thick.
Description
;74~
HEAT-SEALABLE MULTI-LAYER POLYPROPYLENE
FILM STRUCTURE
This invention relates to a multl-laye~ heat-sealable polypropylene film structure having low fllm to film coefficlent o~
friction over a wide temperature range.
Polypropylene film ls an excellent packaging rnaterlal, but it has a high film-to-film coefficient of friction which makes it difficult to utilize in automatic packaging equipment. Moreover, when polypropylene film is used to wrap a package, such as a cigarette package, and the wrapped film is heat sealed to secure the package, there is a particular tendency for film-to-film sticking if adjacent heat seal regions contact shortly after sealing Both of these problems present particular difficulty in automatic cigarette packaging machines, since present day machines run at from 300-400 packs per minute, which is equivalent to approximately 49m (160 ft.) of film per minute. This speed makes it very critical that the coefficient of friction of the film is very low, even after heat sealing of the film.
Certain innovations have improved the surface friction characteristics of polypropylene film. For example, U.S. Patent No.
3,176,021 discloses the inclusion of minor quantities of fatty acid amides into polypropylene film. However, in order to obtain the benefits taught by this patent, certain limitations must be observed. Thus, the film must be formed from a melt, and extruded at a temperature between about 204 to 288C (400F-550F). In addition, the amide must be present in from 0.005 to 2.0 weight percent of the polypropylene and together with from 0.1 to 4.0 weight percent polyethylene. Under these conditions and limitations the resulting polypropylene film will have a static coefficient of friction no higher than 0.6, but this is significantly higher than the 0.25 maximum needed for successful operation in modern high speed ~7~
packaging machines. Further, it has been found that once the film has been subjected to the high temperatures used to effect heat sealing, the coefficient of friction increases signi-ficantly.
U.S. Pa-tent ~o. 3,~99,156 discloses that the incluslon o~
the combination of silicone oil and finely divided sili.ca into a polypropylene Film produces a Film which will have a coefflcLent o-~friction of from 0.45 to 0.46 and be suitable for use in bread-wrapping machines.
It has been found that to a certain extent high crystallinity in polypropylene impedes facile migration of additives to the surface of such a polymer in film form~ This problem is addressed in U.S. Patent No. 4,419,410, which teaches the coextrusion of a skin layer of polypropylene of comparatively low stereoregularity with a core layer of polypropylene of comparatively high stereoregularity. By including in the core layer a surface modifying agent such as an amide of a fatty acid, it is found that the amide blooms to the surface of the comparatively low stereoregularity polymer to lower the coefficient of friction of the film.
In spite of these teachings, it remained until U.S. Patent No. 4,419,411 to significantly advance the art of making multi-layer polypropylene films suitable for most packaging operations. This patent teaches a multi-layer polypropylene film structure having surface modifying agents comprising finely divided silica, silicone oil and an amide of a water insoluble mono-carboxylic acid having from about 8 to about 24 carbon atoms on a surface thereof.
Notwithstanding the general excellence of this film, it is found that when used in high speed cigarette pack wrapping machines, there is a tendency for the film surfaces of contacting packages to stick together, particularly in the areas where heat sealing has occurred.
It is an object of the present invention to provide a multi-layer polypropylene film structure having an extremely low -coefficient of friction over a wide temperature range.
`- ~2~74~ -F-317~ ~~3~~
Accordingly, the present inv~ntion is directed to arl oriented multi-layer film structure comprising coextruded layers of:
(a) a base layer comprising polypropylene o~ relatively high stereo-regularity and ~rom 0.05-0.2% of a long chain aliphatic tertiary amine by weight of the base layer; and ~ b) a heat-sealable skin layer comprising a polyolefin oF
relatively low stereo-regulariky on at least one sur~ace o~ (a), said skin layer containln~ a combination o~ ~inely divi~ed silioa, and a silicone oil, said skin layer being o-~ a thickness less than 0.8 microns and the surface of the skin layer having thereon at least some o~ said amine which has migrated from the base layer (a).
In the multi-layer film structure of the invention, the base layer is an oriented highly crystalline or highly stereoregular polypropylene film which preferably has the ~ollowing properties:
a melt flow rate at 23ûC (446~F.) ranging from 1 to 25, preferably 2 to 4, a crystalline melting point is of 161-163C
(321-325F.), a number average molecular weight from 25,000 to loo,ooo, and a density from o.90 to 0.91.
Included in the base layerp~is a long chain aliphatic tertiary amine, ~or example of the general formula R3N, wherein one of the R groups is a ~atty acid residue or its C12-C18 alkyl equivalent. and the others are hydroxy Cl-C4 alkyl groups. An example of such a compound is N,N-bis(2-hydroxyethyl) tallow amine, wherein the tallow group is believed to include a mixture of C14-C18 alkyl groups. The long chain alkyl groups can also be obtained as mixtures from, for example, coconut oil, fatty acids, and the like. The low molecular weight hydroxy alkyl group can be hydroxyethyl1 hydroxypropyl and hydroxybutyl.
~. ., .~
F-3173 --4~-The amine can be dry blended together wlth the polypropylene resin and then melt mixed. Alternatively, ~he amine can be incorporated into a minor portion of the polypropylene as a master batch to ~orm a high concentration mix of the am~ne an~ ~he polypropylene. This may then be dllute~ to th0 approp~iate proportion by the ad~ition o~ ~nore polypropylene. Althou~h some o~
~hese amines are known anti-static agents, they are employed herein in order to reduce the coefficient of friction of the final film structure and to inhibit package to package sticking. While the amine is added to the base layer resin, when the resin is coextruded with a skin polymer some portion of the amine enters into and moves to the surface of the skin layer. Thus, by this mechanism the amine is available at the surface of the skin layer or layers so as to beneficially affect, in combination with the silica and siloxane, the coefficient of friction and anti-stick characteristics of the multi-layer film.
The relatively low stereoregular polyolefin polymers which can be used as the skin materials of the multi-layer film include, for example, random co-polymers of ethylene and propylene and ethylene-propylene-butene-l terpolymers. The terpolymer preferably contains 3-6 wt % ethylene and 4-5 wt % bute~e~l. However, particularly preferred skin layer polymers are ethylene-propylene copolymers which contain from 2 to 7 wt. % and, more pre~erably, ~rom 3 to 5 wt.% ethylene and which have a melt flow rate at 2~0C
(446F.) from 2 to 15, preferably 3 to 8, a crystalline melting point of 125 to 150C (257. to 302F.), a number average molecular weight from 25~000 to 100,000, and a density from 0.89 to 0.90.
These copolymers have excellent heat seal characteristics, moisture barrier9 stiffness, high strength, good optical properties, but do not possess the excellent physical characteristics in~erent in the polypropylene layer. More~ver,in order to take advantage of its excellent heat seal characteristics~ the skin layer must be modified so as to improve its coefficient of friction and non-stick properties, particularly after being exposed to heat-seal temperatures.
.. ' `
. .
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F-~173 --5--The present invention is based upon-the discovery that the combination of the three surface modifying agents, i.e. khe silica, the silicone oil, and the amine by virtue of its transpork and blooming onto khe surface of the skin layer, produces unexpected improvement in the coefficient of friction and anki-sti~k properkies of the Film structure provided the thickn~s~ of the .skln layer(s) is less than 0.8 microns. These improvernents are retained when the film is used in high speed machines and the film undergoes heat-sealing.
The silica employed can be any commercially available finely divided silica, preferably that having a mean particle size ranging from 0.5 to 5 microns. The silica car, be presenk from 0.05 to 0.5 wt.%, preferably 0.1 to 0.3 wt.% of the skin layer.
The silicone oil, which preferably is a poly-dimethylsiloxane, conveniently has a viscosity of 20,000 to 3,000,000, preferably 20,000 to 30,000 centistokes. This siloxane can be present from 0.3 to 0.8 wt. % of the skin layer.
An optional and preferred modifying agent for use herein is an amide of a water-insoluble monocarboxylic acid having 8 to 24 carbon atoms and mixtures of said amides. Specific examples of this class of amides are erucamide, oleamide, stearamide and behenamide.
It is preferred that this additive be included in the highly stereoregular polypropyIene base layer in an amount of 300 to 400 parts per million of the base layer and/or in the skin layer in an amount up to 2,000 ppm. It is to be understood that the amide slip agent may be provided in the comparatively low stereoregular copolymer skin layer of the finished film by dispersing the amide in the resin precursor of the comparatively high stereoregular polypropylene alone, the amide then exuding from the base or core film through the copolymer film to its surface. Thus, amide additive in the outer film resin starting material is not necessary, but may be desired.
~ ~7~
By using the above surface modifying additives, it is possiole to produce a multi-layer film structure in which the coefficient of friction of the surface of the or each skin layer i5 about 0.25 and is maintained at less -than 0.8 wt ~ to about 132C
(270F). To further aid the heat seal characteristic~ and l~npr~v~
the optical properties of ~he Fi~m, the skl~ layer can also contain up to 10 wt.% of a natural or synthetic terpene resin, a wax, or a low molecular weight (e.g. lO,000) polyethylene.
The overall thickness of the contemplated multi-layer structure is primarily composed of the highly stereoregular polypropylene base layer. The coextruded layer of comparatively low stereoregularity may be present on one or both surfaces of the base layer. It is preferred that the skin layer be on both sides of the base layer and it is critical that the thickness of each skin layer be less than 0.8 microns. So long as the continuity of the film is maintained, the minimum thic~ness of the skin layer is not important, although in practice the skin ~ayer will preferably have a thickness of at least 0.3 microns.
The multi-layer films of the present invention can be prepared employing commercially available systems for coextruding resins. The polypropylene homopolymer of comparatively high stereoregularity containing the tertiary amine and, if desired the amide slip agent, can be coextruded with an ethylene~propylene random copolymer of comparatively low stereoregularity containing the appropriate percentage of the combination of silica and dimethylsiloxane. The polymers can be brought to the molten state and coextruded from a conventional extruder through a flat sheet die, the melt streams being combined in an adapter prior to being extruded from the die. After leaving the die orifice, the multi-layer film structure is chilled and the quenched sheet then conveniently reheated and stretched, e.g., 4 to 6 times in the machine direction (MD), and subsequently, for example, 4 to lO times in the transverse direction (TD). The edges of the film can be ., , : .. .... .. - ,.~-. ~... .- ,, . .,:. ~. . .
. 12~7~6~
trimmed and the film wound onto a core. It is preferred, particularly where the ~ilm contains an amide slip agent, that the thus formed structure be conditioned or equilibrated by holding the same for a period of about 6 hours ko 1 week at a ternperature of 27 to 52C. (80 to 125F ), pre~erably For 6 to 72 hrs. at ~-52~C
(lOû-125F). This Film wlll have on the surFace thereof a combination of the four addikives: amine, amide, silica and silicone oil. The resulting ~ilm will have a coefficient of ~riction of 0.25 or lower and will not block under conditions of tight winding after being held at temperatures up to 60C (140F).
Some commercially available core polymers, skin polymers and incompatible polymers and their at least approximate ~eltin3 points are tabulated below:
TABLE
PolYmeric Material Melting Point Homopolypropylene 161-163C (321-325F) ARCû W756 (ethylene-propylene random 140C (273F) copolymer 3.3-3.6 wt.% ethylene) ARCû 827 (ethylene-propylene random 124C (255F) copolymer 4-8 wt.% ethylene) **
"Chisso XF" 7500 (ethylene-propylene- 130C (266F) butene-l terpolymer, 3.5 wt.% ethylene, 4.5 wt.%
butene-l) ***
'r~hisso XF" 7700 ~ethylene-propylene- 121C (250F) butene-l terpolymer, 5 wt.% ethylene, 4.5 wt.%
butene-l) " Solvay KS 400 ~ethylene-propylene random 132C (270F) copolymer) "Solvay KS 409"~ethylene-propylene random 132C (270F) copolymer 3.4-4.0 wt.~ ethylene) "Sumitomo F~ 6711' ~ethylene-propylene 124C (255F) random copolymer, 4-6% ethylene) * Trademark ** Trademark *** Trademark 1-3 inclusive. The berms bearing these numerals are trademarks.
: ,:, ,,., :..
, ~.., , ..
~ ~7'~t;~ --The invention will now be described with reference to the following examples, in which the films are tested by feediny a rall of film into a"Scandia Model 712"Cigarette Pack Wrapping system with the capability of wrappin~ up to 2 W packs of ci~arettcs per mlnute. During ~ranspo~t throucJh the system each pack :Ls subJect~
to three heat seal regions which can cause package to package sticking~ The film must maintain a coefficient of friction roorn temperature of between about 0.2-0.~ in order to avoid unacceptable drag whlch would lead to pack jamming and machine down-time.
Success of the operation depends on the virtual absence of pack-to-pack sticking, a moderate to low force necessary to move the packs through the system and a seal range of at least 11C (20F), preferably 17-22C (30-40~F), on all seal surfaces.
EXAMPLES
Example 1 A polypropylene homopolymer of comparatively high stereoregularity, i.e.~Novamont 243.4~', containing about l,000 ppm of N,N-bis(2-hydroxyethyl) tallow amine is melt coextruded with skin layers of"Solvay KS 409', an ethylene-propylene copolymer having from about 3.4 4 0 wt.% ethylene, said copolymer containing 6,000 ppm of a poly-dimethylsiloxane, having a viscosity of 30,000 centistokes and 2,000 ppm silica of a mean particle size of about 1-2 micron.
The resulting film has an overall thickness of 21 microns with the core layer being 19.8 microns and the skin layers being 0.6 microns each. Utilizing the above-described multilayer film, cigarette packages can be wrapped using the above-described apparatus at a rate of approximately 172 packs per minute. This wrapping was successfully accomplished with a virtual absence of package-to-package sticking, and with a moderate to low force being necessary to move the packages through the machine system. The permissible temperature range for all seal surfaces was at least 20C.
* Trademark ** Trademark - *** Trademark ~ ~S37~
F-3173 --9-~
Example 1 was repeated except the base polypropylene homopolymex wasl'Novamont ~43.4'lwhich dld not contain any amine.
This film when employed ln the same clcJarette paekaye wrapping system described above showed an increase in drag ~orce through the system uf approximakely 30%.
Example 3 Example 1 was repeated except that the silica was excluded. Employing the resulting film in the same cigarette wrapping system resulted ln jamming of the system in less than one minute due to package to package sticking and increased drag.
Example 4 Example 1 was repeated except that the poly-dimethylsiloxane was excluded. Employing the resulting film in the same cigarette wrapping system again caused the system to jam in - less than one minute due to package to package sticking and increased drag.
Example_5 Example 1 was repeated except the thickness of the skin layer was 0.9 microns each.
This film when employed in the same cigarette package wrapping system described above showed excessive drag sufficient to cause jamming within a few seconds.
* Trademark .~
3~4~i~
F-3173 --10-~
Example 6 The amine-containing polypropylene homopolymer of comparatively high stereoregularity, i.e. Novamont 243.4A, was melt coe~truded with skin layers of Chisso 7500, a ~erpolymer o~
ethylene-propylene-butene-l, said terpolyrner con~ainlng approximately 800 par~s per million oP erl~camide, 6,00~ parts per million of a dimethylpolysiloxane, having a viscosity of 30,000 centistokes and 2,000 parts per million silica of amine particle size of from about 1-2 microns. The resulting film had an overall thickness of 21 microns with the core layer being 19.8 microns and the skin layers 0.5 microns each. Utilizing the above-described multilayer film, cigarette packages, could be wrapped using the above-described apparatus at a xate of approximately 172 packs per minute. This wrapping was successfully accomplished with a virtual absence of package-to-package sticking, with a moderate to low force being necessary to move the packages through the machine. Again, a heat seal range of at least 20C was permissible on all seal surfaces.
Example 7 Example 6 was repeated except the amine was omitted from the polypropylene base layer. Again, the film exhibited an increased drag of about 30% when used in the wrapping apparatus.
Example 8 Example 6 was repeated on two film samples except that in one sample the silica was omitted from the skin layer and in the other sample the silicone oil was omitted. Employing each of the resulting films in the same cigarette package wrapping system described above resulted in jamming of the system in less than one minute due to package to package sticking and increased drag.
~ Z~7~
Example 9 Example 6 was repeated except that the thickness o~ the skin layers was lncreased to 0.9 mi~rons. Ernployiny the resulting ~ilm in tne same cigarette wrappincJ systern as clescrlbed above, resulting in the system Jarnmlng wlthin a ~ew seconds due to package to package sticking and increased drag.
Example 10 Example 6 was repeated except Chisso XF7700 was employed instead of Chisso XF7500 and the skin layers contained 8000 ppm of poly-dimethylsiloxane. The same degree oF wrapping success was experienced as in Example 6.
HEAT-SEALABLE MULTI-LAYER POLYPROPYLENE
FILM STRUCTURE
This invention relates to a multl-laye~ heat-sealable polypropylene film structure having low fllm to film coefficlent o~
friction over a wide temperature range.
Polypropylene film ls an excellent packaging rnaterlal, but it has a high film-to-film coefficient of friction which makes it difficult to utilize in automatic packaging equipment. Moreover, when polypropylene film is used to wrap a package, such as a cigarette package, and the wrapped film is heat sealed to secure the package, there is a particular tendency for film-to-film sticking if adjacent heat seal regions contact shortly after sealing Both of these problems present particular difficulty in automatic cigarette packaging machines, since present day machines run at from 300-400 packs per minute, which is equivalent to approximately 49m (160 ft.) of film per minute. This speed makes it very critical that the coefficient of friction of the film is very low, even after heat sealing of the film.
Certain innovations have improved the surface friction characteristics of polypropylene film. For example, U.S. Patent No.
3,176,021 discloses the inclusion of minor quantities of fatty acid amides into polypropylene film. However, in order to obtain the benefits taught by this patent, certain limitations must be observed. Thus, the film must be formed from a melt, and extruded at a temperature between about 204 to 288C (400F-550F). In addition, the amide must be present in from 0.005 to 2.0 weight percent of the polypropylene and together with from 0.1 to 4.0 weight percent polyethylene. Under these conditions and limitations the resulting polypropylene film will have a static coefficient of friction no higher than 0.6, but this is significantly higher than the 0.25 maximum needed for successful operation in modern high speed ~7~
packaging machines. Further, it has been found that once the film has been subjected to the high temperatures used to effect heat sealing, the coefficient of friction increases signi-ficantly.
U.S. Pa-tent ~o. 3,~99,156 discloses that the incluslon o~
the combination of silicone oil and finely divided sili.ca into a polypropylene Film produces a Film which will have a coefflcLent o-~friction of from 0.45 to 0.46 and be suitable for use in bread-wrapping machines.
It has been found that to a certain extent high crystallinity in polypropylene impedes facile migration of additives to the surface of such a polymer in film form~ This problem is addressed in U.S. Patent No. 4,419,410, which teaches the coextrusion of a skin layer of polypropylene of comparatively low stereoregularity with a core layer of polypropylene of comparatively high stereoregularity. By including in the core layer a surface modifying agent such as an amide of a fatty acid, it is found that the amide blooms to the surface of the comparatively low stereoregularity polymer to lower the coefficient of friction of the film.
In spite of these teachings, it remained until U.S. Patent No. 4,419,411 to significantly advance the art of making multi-layer polypropylene films suitable for most packaging operations. This patent teaches a multi-layer polypropylene film structure having surface modifying agents comprising finely divided silica, silicone oil and an amide of a water insoluble mono-carboxylic acid having from about 8 to about 24 carbon atoms on a surface thereof.
Notwithstanding the general excellence of this film, it is found that when used in high speed cigarette pack wrapping machines, there is a tendency for the film surfaces of contacting packages to stick together, particularly in the areas where heat sealing has occurred.
It is an object of the present invention to provide a multi-layer polypropylene film structure having an extremely low -coefficient of friction over a wide temperature range.
`- ~2~74~ -F-317~ ~~3~~
Accordingly, the present inv~ntion is directed to arl oriented multi-layer film structure comprising coextruded layers of:
(a) a base layer comprising polypropylene o~ relatively high stereo-regularity and ~rom 0.05-0.2% of a long chain aliphatic tertiary amine by weight of the base layer; and ~ b) a heat-sealable skin layer comprising a polyolefin oF
relatively low stereo-regulariky on at least one sur~ace o~ (a), said skin layer containln~ a combination o~ ~inely divi~ed silioa, and a silicone oil, said skin layer being o-~ a thickness less than 0.8 microns and the surface of the skin layer having thereon at least some o~ said amine which has migrated from the base layer (a).
In the multi-layer film structure of the invention, the base layer is an oriented highly crystalline or highly stereoregular polypropylene film which preferably has the ~ollowing properties:
a melt flow rate at 23ûC (446~F.) ranging from 1 to 25, preferably 2 to 4, a crystalline melting point is of 161-163C
(321-325F.), a number average molecular weight from 25,000 to loo,ooo, and a density from o.90 to 0.91.
Included in the base layerp~is a long chain aliphatic tertiary amine, ~or example of the general formula R3N, wherein one of the R groups is a ~atty acid residue or its C12-C18 alkyl equivalent. and the others are hydroxy Cl-C4 alkyl groups. An example of such a compound is N,N-bis(2-hydroxyethyl) tallow amine, wherein the tallow group is believed to include a mixture of C14-C18 alkyl groups. The long chain alkyl groups can also be obtained as mixtures from, for example, coconut oil, fatty acids, and the like. The low molecular weight hydroxy alkyl group can be hydroxyethyl1 hydroxypropyl and hydroxybutyl.
~. ., .~
F-3173 --4~-The amine can be dry blended together wlth the polypropylene resin and then melt mixed. Alternatively, ~he amine can be incorporated into a minor portion of the polypropylene as a master batch to ~orm a high concentration mix of the am~ne an~ ~he polypropylene. This may then be dllute~ to th0 approp~iate proportion by the ad~ition o~ ~nore polypropylene. Althou~h some o~
~hese amines are known anti-static agents, they are employed herein in order to reduce the coefficient of friction of the final film structure and to inhibit package to package sticking. While the amine is added to the base layer resin, when the resin is coextruded with a skin polymer some portion of the amine enters into and moves to the surface of the skin layer. Thus, by this mechanism the amine is available at the surface of the skin layer or layers so as to beneficially affect, in combination with the silica and siloxane, the coefficient of friction and anti-stick characteristics of the multi-layer film.
The relatively low stereoregular polyolefin polymers which can be used as the skin materials of the multi-layer film include, for example, random co-polymers of ethylene and propylene and ethylene-propylene-butene-l terpolymers. The terpolymer preferably contains 3-6 wt % ethylene and 4-5 wt % bute~e~l. However, particularly preferred skin layer polymers are ethylene-propylene copolymers which contain from 2 to 7 wt. % and, more pre~erably, ~rom 3 to 5 wt.% ethylene and which have a melt flow rate at 2~0C
(446F.) from 2 to 15, preferably 3 to 8, a crystalline melting point of 125 to 150C (257. to 302F.), a number average molecular weight from 25~000 to 100,000, and a density from 0.89 to 0.90.
These copolymers have excellent heat seal characteristics, moisture barrier9 stiffness, high strength, good optical properties, but do not possess the excellent physical characteristics in~erent in the polypropylene layer. More~ver,in order to take advantage of its excellent heat seal characteristics~ the skin layer must be modified so as to improve its coefficient of friction and non-stick properties, particularly after being exposed to heat-seal temperatures.
.. ' `
. .
6~
F-~173 --5--The present invention is based upon-the discovery that the combination of the three surface modifying agents, i.e. khe silica, the silicone oil, and the amine by virtue of its transpork and blooming onto khe surface of the skin layer, produces unexpected improvement in the coefficient of friction and anki-sti~k properkies of the Film structure provided the thickn~s~ of the .skln layer(s) is less than 0.8 microns. These improvernents are retained when the film is used in high speed machines and the film undergoes heat-sealing.
The silica employed can be any commercially available finely divided silica, preferably that having a mean particle size ranging from 0.5 to 5 microns. The silica car, be presenk from 0.05 to 0.5 wt.%, preferably 0.1 to 0.3 wt.% of the skin layer.
The silicone oil, which preferably is a poly-dimethylsiloxane, conveniently has a viscosity of 20,000 to 3,000,000, preferably 20,000 to 30,000 centistokes. This siloxane can be present from 0.3 to 0.8 wt. % of the skin layer.
An optional and preferred modifying agent for use herein is an amide of a water-insoluble monocarboxylic acid having 8 to 24 carbon atoms and mixtures of said amides. Specific examples of this class of amides are erucamide, oleamide, stearamide and behenamide.
It is preferred that this additive be included in the highly stereoregular polypropyIene base layer in an amount of 300 to 400 parts per million of the base layer and/or in the skin layer in an amount up to 2,000 ppm. It is to be understood that the amide slip agent may be provided in the comparatively low stereoregular copolymer skin layer of the finished film by dispersing the amide in the resin precursor of the comparatively high stereoregular polypropylene alone, the amide then exuding from the base or core film through the copolymer film to its surface. Thus, amide additive in the outer film resin starting material is not necessary, but may be desired.
~ ~7~
By using the above surface modifying additives, it is possiole to produce a multi-layer film structure in which the coefficient of friction of the surface of the or each skin layer i5 about 0.25 and is maintained at less -than 0.8 wt ~ to about 132C
(270F). To further aid the heat seal characteristic~ and l~npr~v~
the optical properties of ~he Fi~m, the skl~ layer can also contain up to 10 wt.% of a natural or synthetic terpene resin, a wax, or a low molecular weight (e.g. lO,000) polyethylene.
The overall thickness of the contemplated multi-layer structure is primarily composed of the highly stereoregular polypropylene base layer. The coextruded layer of comparatively low stereoregularity may be present on one or both surfaces of the base layer. It is preferred that the skin layer be on both sides of the base layer and it is critical that the thickness of each skin layer be less than 0.8 microns. So long as the continuity of the film is maintained, the minimum thic~ness of the skin layer is not important, although in practice the skin ~ayer will preferably have a thickness of at least 0.3 microns.
The multi-layer films of the present invention can be prepared employing commercially available systems for coextruding resins. The polypropylene homopolymer of comparatively high stereoregularity containing the tertiary amine and, if desired the amide slip agent, can be coextruded with an ethylene~propylene random copolymer of comparatively low stereoregularity containing the appropriate percentage of the combination of silica and dimethylsiloxane. The polymers can be brought to the molten state and coextruded from a conventional extruder through a flat sheet die, the melt streams being combined in an adapter prior to being extruded from the die. After leaving the die orifice, the multi-layer film structure is chilled and the quenched sheet then conveniently reheated and stretched, e.g., 4 to 6 times in the machine direction (MD), and subsequently, for example, 4 to lO times in the transverse direction (TD). The edges of the film can be ., , : .. .... .. - ,.~-. ~... .- ,, . .,:. ~. . .
. 12~7~6~
trimmed and the film wound onto a core. It is preferred, particularly where the ~ilm contains an amide slip agent, that the thus formed structure be conditioned or equilibrated by holding the same for a period of about 6 hours ko 1 week at a ternperature of 27 to 52C. (80 to 125F ), pre~erably For 6 to 72 hrs. at ~-52~C
(lOû-125F). This Film wlll have on the surFace thereof a combination of the four addikives: amine, amide, silica and silicone oil. The resulting ~ilm will have a coefficient of ~riction of 0.25 or lower and will not block under conditions of tight winding after being held at temperatures up to 60C (140F).
Some commercially available core polymers, skin polymers and incompatible polymers and their at least approximate ~eltin3 points are tabulated below:
TABLE
PolYmeric Material Melting Point Homopolypropylene 161-163C (321-325F) ARCû W756 (ethylene-propylene random 140C (273F) copolymer 3.3-3.6 wt.% ethylene) ARCû 827 (ethylene-propylene random 124C (255F) copolymer 4-8 wt.% ethylene) **
"Chisso XF" 7500 (ethylene-propylene- 130C (266F) butene-l terpolymer, 3.5 wt.% ethylene, 4.5 wt.%
butene-l) ***
'r~hisso XF" 7700 ~ethylene-propylene- 121C (250F) butene-l terpolymer, 5 wt.% ethylene, 4.5 wt.%
butene-l) " Solvay KS 400 ~ethylene-propylene random 132C (270F) copolymer) "Solvay KS 409"~ethylene-propylene random 132C (270F) copolymer 3.4-4.0 wt.~ ethylene) "Sumitomo F~ 6711' ~ethylene-propylene 124C (255F) random copolymer, 4-6% ethylene) * Trademark ** Trademark *** Trademark 1-3 inclusive. The berms bearing these numerals are trademarks.
: ,:, ,,., :..
, ~.., , ..
~ ~7'~t;~ --The invention will now be described with reference to the following examples, in which the films are tested by feediny a rall of film into a"Scandia Model 712"Cigarette Pack Wrapping system with the capability of wrappin~ up to 2 W packs of ci~arettcs per mlnute. During ~ranspo~t throucJh the system each pack :Ls subJect~
to three heat seal regions which can cause package to package sticking~ The film must maintain a coefficient of friction roorn temperature of between about 0.2-0.~ in order to avoid unacceptable drag whlch would lead to pack jamming and machine down-time.
Success of the operation depends on the virtual absence of pack-to-pack sticking, a moderate to low force necessary to move the packs through the system and a seal range of at least 11C (20F), preferably 17-22C (30-40~F), on all seal surfaces.
EXAMPLES
Example 1 A polypropylene homopolymer of comparatively high stereoregularity, i.e.~Novamont 243.4~', containing about l,000 ppm of N,N-bis(2-hydroxyethyl) tallow amine is melt coextruded with skin layers of"Solvay KS 409', an ethylene-propylene copolymer having from about 3.4 4 0 wt.% ethylene, said copolymer containing 6,000 ppm of a poly-dimethylsiloxane, having a viscosity of 30,000 centistokes and 2,000 ppm silica of a mean particle size of about 1-2 micron.
The resulting film has an overall thickness of 21 microns with the core layer being 19.8 microns and the skin layers being 0.6 microns each. Utilizing the above-described multilayer film, cigarette packages can be wrapped using the above-described apparatus at a rate of approximately 172 packs per minute. This wrapping was successfully accomplished with a virtual absence of package-to-package sticking, and with a moderate to low force being necessary to move the packages through the machine system. The permissible temperature range for all seal surfaces was at least 20C.
* Trademark ** Trademark - *** Trademark ~ ~S37~
F-3173 --9-~
Example 1 was repeated except the base polypropylene homopolymex wasl'Novamont ~43.4'lwhich dld not contain any amine.
This film when employed ln the same clcJarette paekaye wrapping system described above showed an increase in drag ~orce through the system uf approximakely 30%.
Example 3 Example 1 was repeated except that the silica was excluded. Employing the resulting film in the same cigarette wrapping system resulted ln jamming of the system in less than one minute due to package to package sticking and increased drag.
Example 4 Example 1 was repeated except that the poly-dimethylsiloxane was excluded. Employing the resulting film in the same cigarette wrapping system again caused the system to jam in - less than one minute due to package to package sticking and increased drag.
Example_5 Example 1 was repeated except the thickness of the skin layer was 0.9 microns each.
This film when employed in the same cigarette package wrapping system described above showed excessive drag sufficient to cause jamming within a few seconds.
* Trademark .~
3~4~i~
F-3173 --10-~
Example 6 The amine-containing polypropylene homopolymer of comparatively high stereoregularity, i.e. Novamont 243.4A, was melt coe~truded with skin layers of Chisso 7500, a ~erpolymer o~
ethylene-propylene-butene-l, said terpolyrner con~ainlng approximately 800 par~s per million oP erl~camide, 6,00~ parts per million of a dimethylpolysiloxane, having a viscosity of 30,000 centistokes and 2,000 parts per million silica of amine particle size of from about 1-2 microns. The resulting film had an overall thickness of 21 microns with the core layer being 19.8 microns and the skin layers 0.5 microns each. Utilizing the above-described multilayer film, cigarette packages, could be wrapped using the above-described apparatus at a xate of approximately 172 packs per minute. This wrapping was successfully accomplished with a virtual absence of package-to-package sticking, with a moderate to low force being necessary to move the packages through the machine. Again, a heat seal range of at least 20C was permissible on all seal surfaces.
Example 7 Example 6 was repeated except the amine was omitted from the polypropylene base layer. Again, the film exhibited an increased drag of about 30% when used in the wrapping apparatus.
Example 8 Example 6 was repeated on two film samples except that in one sample the silica was omitted from the skin layer and in the other sample the silicone oil was omitted. Employing each of the resulting films in the same cigarette package wrapping system described above resulted in jamming of the system in less than one minute due to package to package sticking and increased drag.
~ Z~7~
Example 9 Example 6 was repeated except that the thickness o~ the skin layers was lncreased to 0.9 mi~rons. Ernployiny the resulting ~ilm in tne same cigarette wrappincJ systern as clescrlbed above, resulting in the system Jarnmlng wlthin a ~ew seconds due to package to package sticking and increased drag.
Example 10 Example 6 was repeated except Chisso XF7700 was employed instead of Chisso XF7500 and the skin layers contained 8000 ppm of poly-dimethylsiloxane. The same degree oF wrapping success was experienced as in Example 6.
Claims (8)
1. An oriented multi-layer film structure comprising coextruded layers of:
(a) a base layer comprising polypropylene of relatively high stereoregularity and 0.05-0.2 % of a long chain aliphatic tertiary amine by weight of the base layer; and (b) a heat-sealable skin layer comprising a polyolefin of relatively low stereoregularity on at least one surface of (a), said skin layer containing a combination of finely divided silica and a silicone oil and said skin layer having a thickness less than about 0.8 microns.
(a) a base layer comprising polypropylene of relatively high stereoregularity and 0.05-0.2 % of a long chain aliphatic tertiary amine by weight of the base layer; and (b) a heat-sealable skin layer comprising a polyolefin of relatively low stereoregularity on at least one surface of (a), said skin layer containing a combination of finely divided silica and a silicone oil and said skin layer having a thickness less than about 0.8 microns.
2. The structure of claim 1 wherein said amine is of the general formula R3N, with one of the R groups being C12-C18 alkyl group and the others being hydroxy C1-C4 alkyl groups.
3. The structure of claim 1 wherein said polyolefin is either a random copolymer of propylene with ethylene or a terpolymer of propylene with ethylene and butene-l.
4. The structure of claim 3 wherein said copolymer of propylene with ethylene contains from 2 to 8 wt.% ethylene.
5. The structure of claim 3 wherein said terpolymer of propylene with ethylene and butene-1 contains from 3-6 wt.% ethylene and 4-5 wt.% butene-1.
6. The structure of any one of claims 1-3 wherein said silica has a mean particle size of from 0.5 to 5 microns and is present in from 0.05 to 0.5 wt.% of said skin layer.
7. The structure of any of one claims 1-3 wherein said silicone oil is poly-dimethylsiloxane having a viscosity of 20,000 to 3,000,000 centistokes, and is present in from 0.3 to 0.8 wt.% of said skin layer.
8. The structure og any one of claims 1-3 also containing an amide of a water-insoluble monocarboxylic acid having from 8 to 24 carbon atoms wherein said amide is present in the precursor resin of said base layer in from 300 to 400 ppm and in said skin layer in up to 2000 ppm.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US67137684A | 1984-11-14 | 1984-11-14 | |
| US671,376 | 1991-03-19 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1287464C true CA1287464C (en) | 1991-08-13 |
Family
ID=24694279
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000490265A Expired - Lifetime CA1287464C (en) | 1984-11-14 | 1985-09-09 | Heat-sealable multi-layer polypropylene film structure |
Country Status (12)
| Country | Link |
|---|---|
| EP (1) | EP0182463B1 (en) |
| JP (1) | JPS61120744A (en) |
| AT (1) | ATE68410T1 (en) |
| AU (1) | AU593219B2 (en) |
| BR (1) | BR8504506A (en) |
| CA (1) | CA1287464C (en) |
| DE (1) | DE3584418D1 (en) |
| ES (1) | ES8705001A1 (en) |
| GR (1) | GR852284B (en) |
| NZ (1) | NZ213356A (en) |
| TR (1) | TR22657A (en) |
| ZA (1) | ZA857498B (en) |
Families Citing this family (14)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3517795A1 (en) * | 1985-05-17 | 1986-11-20 | Hoechst Ag, 6230 Frankfurt | NON-SEALABLE, BIAXIAL-ORIENTED MULTILAYER FILM FROM PROPYLENE POLYMERS, METHOD FOR PRODUCING THE FILM AND THEIR USE |
| US4764425A (en) * | 1987-01-02 | 1988-08-16 | Mobil Oil Corporation | Oriented, heat sealable multi-layered film |
| US5683802A (en) * | 1994-03-17 | 1997-11-04 | Hoechst Aktiengesellschaft | Heat-seatable or non-heat-sealable, oriented, multilayer polyolefin film comprising ceramic particles |
| DE4426185A1 (en) | 1994-07-23 | 1996-01-25 | Hoechst Ag | Sealable oriented polyolefin multilayer film, process for its production and its use |
| DE19652734A1 (en) * | 1996-12-18 | 1998-06-25 | Hoechst Trespaphan Gmbh | Oriented polyolefin multilayer film which can be sealed on both sides, process for their production and their use |
| KR100648026B1 (en) * | 1998-10-15 | 2006-11-23 | 가부시키가이샤 유포 코포레숀 | Label for in-mold molding |
| US20040151934A1 (en) * | 2003-01-27 | 2004-08-05 | Schwark Dwight W. | Oxygen scavenging film with high slip properties |
| GB0304757D0 (en) * | 2003-03-01 | 2003-04-02 | Rexam Med Packaging Ltd | Polymeric films and packages produced therefrom |
| WO2004089621A1 (en) * | 2003-04-11 | 2004-10-21 | Treofan Germany Gmbh & Co. Kg | Biaxially oriented polypropylene film provided with a cold-seal adhesive coating and having excellent lubricating properties |
| EP1820642A1 (en) * | 2006-02-20 | 2007-08-22 | Syrom 90 S.P.A. | Multilayer plastic film |
| JP2009263440A (en) * | 2008-04-23 | 2009-11-12 | Tosoh Corp | Resin composition for lamination and laminate film |
| GB2491575B (en) | 2011-06-02 | 2013-11-27 | Innovia Films Ltd | Package |
| US20130164516A1 (en) * | 2011-12-22 | 2013-06-27 | E I Du Pont De Nemours And Company | Low temperature sealing films |
| EP3034300B1 (en) | 2014-12-19 | 2018-08-22 | Irplast S.p.A. | Multilayer films |
Family Cites Families (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5312971A (en) * | 1976-07-22 | 1978-02-06 | Honshu Paper Co Ltd | Polypropylene composite film having antistatic and low temperature heat seal property and its production |
| JPS5428351A (en) * | 1977-08-05 | 1979-03-02 | Mitsubishi Petrochem Co Ltd | Readily heat-sealable resin composition and composite film having improved transparency |
| JPS5591665A (en) * | 1978-12-29 | 1980-07-11 | Toyo Boseki | Package of high sealinggup property |
| JPS5549264A (en) * | 1978-10-06 | 1980-04-09 | Toray Industries | Laminated film |
| JPS5942614B2 (en) * | 1979-05-19 | 1984-10-16 | 株式会社トクヤマ | Method for producing laminated biaxially stretched polypropylene film |
| DE2941909A1 (en) * | 1979-10-17 | 1981-04-30 | Wolff Walsrode Ag, 3030 Walsrode | SEALABLE MULTILAYER FILM MADE OF POLYOLEFINES |
| JPS5933308A (en) * | 1982-08-20 | 1984-02-23 | Fukubi Kagaku Kogyo Kk | Production of artificial marble |
| US4419411A (en) * | 1982-12-23 | 1983-12-06 | Mobil Oil Corporation | Multi-layer polypropylene film structure and method of forming same |
| DE3434298A1 (en) * | 1984-09-19 | 1986-03-27 | Hoechst Ag, 6230 Frankfurt | TRANSFER METALIZING FILM |
| US4604324A (en) * | 1984-09-28 | 1986-08-05 | Mobil Oil Corporation | Multi-layer polypropylene film structure and method of forming the same |
-
1985
- 1985-09-04 NZ NZ213356A patent/NZ213356A/en unknown
- 1985-09-06 AU AU47138/85A patent/AU593219B2/en not_active Ceased
- 1985-09-06 DE DE8585306343T patent/DE3584418D1/en not_active Revoked
- 1985-09-06 EP EP85306343A patent/EP0182463B1/en not_active Expired - Lifetime
- 1985-09-06 AT AT85306343T patent/ATE68410T1/en not_active IP Right Cessation
- 1985-09-09 CA CA000490265A patent/CA1287464C/en not_active Expired - Lifetime
- 1985-09-16 BR BR8504506A patent/BR8504506A/en unknown
- 1985-09-19 GR GR852284A patent/GR852284B/el unknown
- 1985-09-20 JP JP60208538A patent/JPS61120744A/en active Granted
- 1985-09-25 TR TR39354A patent/TR22657A/en unknown
- 1985-09-26 ES ES547339A patent/ES8705001A1/en not_active Expired
- 1985-09-27 ZA ZA857498A patent/ZA857498B/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| AU4713885A (en) | 1986-05-22 |
| EP0182463A3 (en) | 1987-09-23 |
| ES547339A0 (en) | 1987-04-16 |
| ES8705001A1 (en) | 1987-04-16 |
| AU593219B2 (en) | 1990-02-08 |
| DE3584418D1 (en) | 1991-11-21 |
| ZA857498B (en) | 1987-05-27 |
| GR852284B (en) | 1986-01-21 |
| EP0182463A2 (en) | 1986-05-28 |
| ATE68410T1 (en) | 1991-11-15 |
| BR8504506A (en) | 1986-07-15 |
| TR22657A (en) | 1988-02-03 |
| JPH0477665B2 (en) | 1992-12-09 |
| NZ213356A (en) | 1989-01-06 |
| EP0182463B1 (en) | 1991-10-16 |
| JPS61120744A (en) | 1986-06-07 |
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